The use of metastable afterglow species to excite sample atoms, molecules and/or fragments etc. so that identifying radiation is emitted thereby when they relax is known. Existing systems for use in practicing sample analysis techniques which utilize metastable afterglow species, however, typically provide for formation of said metastable afterglow species within a tube or the like which is made from oxygen containing materials. Continuing, formation of metastable afterglow species inside said tube or the like is typically by electric discharge. This is mentioned as said electric discharge commonly causes oxygen atoms and molecules etc. to be sputtered from the inner surface of said tube or the like. The presence of said oxygen atoms and molecules etc. can lead to sample analysis complicating oxygen contamination. It should also be appreciated that use of tubes or the like made from, or lined with, other materials can likewise lead to sample contamination by elements other than oxygen contained in, and sputtered from, said other materials during electric discharge.
It should be appearant that when sample identifying radiation, originating when energy released from metastable afterglow species interacts with closely situated sample molecules, atoms and/or other fragments is to be analyzed said radiation must escape from the tube or the like in which said metastable afterglow species and sample are contained and enter a radiation analysis system detector. This requires that said tube or the like of said sample excitation detector system provide, at a minimum, a window area which is transparent to said radiation. Said window must also be located so that it can conveniently couple said escaping sample identifying radiation to said radiation analysis system detector. Design of sample excitation detector systems must therefore be undertaken with radiation analysis system geometry in mind. This is to be understood in view of the fact that different radiation analysis systems have different geometries thereby making inter-changability of sample excitation detector systems there-amoungst difficult.
It is also mentioned that when electric discharge takes place inside an electric discharge chamber, carbon is formed Therein. Carbon can build-up inside an electric discharge system and serve to adversely effect sample analysis results mediated thereby.
In view of the above it should be appreciated that a system for generating metastable afterglow species which is made at least in part from a non-oxygen containing material, which non-oxygen containing material is essentially transparent to radiation emitted by sample atoms, molecules and/or fragments etc. excited inside said system by interaction with energy released from said metastable afterglow species created therein, would be of great utility. Not only could oxygen contamination of sample be avoided, but as well, said system would be relatively easy to design for use with various radiation analysis detector systems. The later attribute resulting because essentially the entire system would allow sample identifying radiation produced therein to escape. As alluded to above, conventional sample excitation detector systems provide only a relatively small window through which sample identifying radiation can escape. In addition, if the non-oxygen containing material is one which contains atoms which easily combine with carbon to form a volatile compound, carbon developed during metastable species creating electric discharge might be easily removed from the electric discharge system in the form of a volatile compound of carbon and atoms sputtered from said non-oxygen material during said electric discharge, instead of depositing inside said tube or the like in which electric discharge takes place. This would provide obvious utility and allow easy cleaning of the system.
A search of Patents has provided a patent, U.S. Pat. No. 2,943,223 to Fay. This Patent describes an elongated hollow dielectric member with closure means at each end thereof, one of which is transparent to radiation produced inside thereof by electric discharge between two elongated electrodes present therein. Gas entry and exit means are also present at opposite extents of the elongated hollow dielectric member.
Another patent, U.S. Pat. No. 4,225,235 to Anderson et al. describes an elongated sample introduction system for flameless emission spectroscopy comprising a reaction chamber which has means for aspirating a sample solution thereinto at one end thereof. Aspirated sample is subjected to energy present in microwave discharge generated metastable species formed from gas injected simultaneous with said aspirated sample. Light collection and focusing optics are also described for use in focusing light emitted by excited sample into a detection system.
A Patent to Braman, U.S. Pat. No. 3,612,686 describes a method and system for spectrochemical analysis of a subject gas introduced by a carrier gas flow into an elongated analysis chamber, which elongated analysis chamber has electrodes present at each end thereof. During use a continuous direct current discharge is typically applied to the electrodes to sustain a plasma in The carrier gas. It is mentioned that the carrier gas utilized should have a high ionization potential, preferably higher than any of the components of a subject gas to be detected. The analysis chamber is described as being comprised of an electrically insulating material through which can pass the frequencies of radiation expected to De radiated. Pyrex brand glass and quartz are given as examples of suitable electrically insulating materials. Gas entry and exit means are present at opposite ends of said elongated analysis chamber.
A Patent to Dahlquist et al., U.S. Pat. No 3,685,911 describes a capillary arc plasma device comprised of a straight tubular passageway with an anode at one end thereof and a and cathode at an opposite end thereof, which cathode is shielded from the anode end of the passageway to minimize transmission of light from the cathode through the passageway and enable end-on spectrometric observation of an arc in the passageway. During use electric discharge is caused to occur between the anode and cathode and sample is entered to the discharge. The use of a lithium fluoride window is identified as a means to allow detection of radiation produced by interaction between the electric discharge and the sample at wavelengths as short as about eleven-hundred (1100) Angstroms.
U.S. Pat. No. 5,117,150 to Schwartz et al. describes a deuterium lamp with a quartz glass bulb for spectral analyzers. At least the portion of the quartz glass bulb through which the radiation passes is provided on its outer surface with a multiple interference filter. The multiple interference filter, which is vapor-deposited, is comprised of alternating aluminum oxide and silicon dioxide or magnesium fluoride. The purpose of the multiple interference filter is to reduce radiation noise
Another Patent, U.S. Pat. No. Re. 33,415 to Jelic describes a double-bore capillary tube gas discharge lamp with an envelope window transparent to short wavelength light. The envelope window is identified as being made of magnesium fluoride.
A Patent to Crawford et al., U.S. Pat. No. 4,898,465 describes a gas analyzing apparatus comprising a quartz tube is housed in a body made from a material with extremely low electrical conductivity and thermal coefficient of expansion, but with high thermal conductivity and machinability. Boron nitride is mentioned as a suitable material. The quartz tube has anode and cathode electrodes at opposite ends thereof for causing a D.C. glow discharge during use. Said quartz tube is also bent so that said anode and cathode are non-colinear. Contaminates entered with sample gas are caused to impinge on the quartz tube at the bend therein and are deposited thereat. A photodetector is coaxially sighted with the downstream leg of the bent pathway. Errors due to fogging of the pathway over time are thus eliminated.
A Patent to Christensen, U.S. Pat. No. 5,062,116 describes a halogen-comparable high-frequency discharge apparatus. Discharge tubes formed of metal fluoride glasses, (note that glasses are amorphous), are used in apparatus for emitting high frequency laser and fluorescent light. The use of metal fluorides glasses serves to make the discharge tubes resistant to corrosion from halogen-containing gas mixtures subjected to high frequency excitation in the apparatus.
Analysis of the Patents cited shows that a need remains for an afterglow electric discharge detector system for use in sample excitation which at once:
a. allows excitation of sample in an electric discharge tube or the like made of, or lined with, a selected material, PA1 b. is predominantly made from a material which is transparent to sample identifying radiation, and PA1 c. is preferably made from a material which can combine with carbon to form volatile compounds so that carbon formed during metastable species forming electrical discharge can be easily removed from the system.
Such a sample excitation system should optionally provide multiple separate electrical discharge pathway(s) which present various materials within which an electrical discharge can occur. Said multiple electrical discharge pathways allowing analysis of samples which contain elements present in other electrical discharge pathways without contamination thereof by sputtered atoms and molecules etc. In addition, the material from which the afterglow electric discharge detector system is constructed should be easily machinable to allow formation thereof into desired configurations.